CH A PY Re eee 
STRUCTURE OF THE LAKE SUPERIOR BASIN. 
Foster and Whitney’s views as to the existence of a synclinal between Isle Royale and Keweenaw 
Point.—Westward extension of the Isle Royale-Keweenaw Point synclinal; first shown to 
exist in 1873.—Course and structure of the synclinal as shown by the work of the Wisconsin 
Geological Survey.—Structure and extent of the synclinal as now worked out.—Parallelism 
between the courses of the Keweenawan belts of the North and South Shores; and of the coast 
lines with these belts.—Explanation of Plates XXVIII and XXIX.—Nature of the bottom of 
the synclinal.—Complications of the synclinal by faulting. 
Foster and Whitney first pointed out the probability that a synclinal 
depression exists, underneath the waters of Lake Superior, between Isle 
Royale and Keweenaw Point,’ being led to this view by the lakeward in- 
clination of the rocks on both Isle Royale and the Point, and by the fact 
that, on the lakeward side of each, sandstone and conglomerate prevail, 
while on the side away from the lake the rock beds in each case are pre- 
vailingly crystalline. 
During my first season’s work on Lake Superior, for the Wisconsin 
State Geological Survey, in 1873, I collected facts in the Bad River country 
of Wisconsin going to show that to the westward the Isle Royale-Kewee- 
naw Point synclinal runs on to the South Shore, the rocks being found there 
dipping both ways. The observations of my assistant, Mr. E. T. Sweet, 
made during the same season on the Copper Range of Douglas County, 
Wisconsin, tended very strongly to confirm this conclusion, since the rocks 
of that range were found to dip southward. My conclusions from the data 
then in hand were published in 1874, along with an outline map and 
section.” The subsequent work of the Wisconsin Survey, during the years 
from 1874 to 1878, by Sweet, Strong, Chamberlin and myself, served to 
place beyond question the truth of the main points of my conclusions of 
1 Report on Lake Superior Land District, Part I, p. 109. 
2“On the Age of the Copper-Bearing Rocks of Lake Superior; and on the Westward Continuation 
of the Lake Superior Synclinal.” American Journal of Science and Arts, Vol. VIII, July, 1874. 
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